1. Field of the Invention
This invention relates to a fine pattern forming material used for forming a pattern by the method of electric charged beam direct writing using electron beam or focused ion beam and thereby producing semiconductor devices or integrated circuits, as well as to a pattern forming method using said material.
2. Description of Prior Art
Hitherto, in the production of IC, LSI, etc., pattern forming has been carried out by photo lithography using ultraviolet rays. As the devices become finer, numerical aperture of stepper lens is becoming higher and the wavelength of light source is becoming shorter. However, these means are disadvantageous in that they bring about a smaller focus depth. Further, the adoption of finer pattern dimension of LSI devices and the production of ASIC have become promoting the use of electron beam lithography. For the fine pattern forming by electron beam lithography, positive type electron beam resist has an indispensable necessity. Although polymethyl methacrylate (PMMA) is known to have the highest resolving power among the positive type electron beam resists, it is disadvantageous in that its sensitivity is low. Thus, a numner of studies have been reported in the recent years concerning the method for improving positive type electron beam resist in sensitivity. For example, positive type electron beam resists made of polybutyl methacrylate, methyl methacrylate-methacrylic acid copolymer, methacrylic acid-acrylonitrile copolymer, methyl methacrylate-isobutylene copolymer, polybutene-1-sulfone, polyisopropenyl ketone, fluoro polymethacrylate, and the like have been disclosed. In all these types of resists, an electron withdrawing group is introduced into the side chain or a readily decomposable group is introduced in the principal chain in order to facilitate the scission of principal chain upon exposure to electron beams and thereby to improve the sensitivity. However, they have a problem that they are poor in dry etch resistance, they are readily influenced by the charging-up phenomenon because of its insulating character, and they are apt to be contaminated by organic solvent developer. Further, electron beam lithography is disadvantageous in that accuracy of pattern can be deteriorated by the proximity effect due to the forward and back scatterings of electron. From the viewpoint of overcoming these disadvantages, the multi-layer resist process wherein the function of resist is divided into that of pattern forming layer and that of planerizing layer is effective. FIGS. 6(a)- 6(d) illustrates a multi-layer resist process in the electron beam lithography. An organic film having a thickness of 2 to 3 microns is formed as a bottom layer 51 for suppressing the proximity effect, on which an inorganic film of SiO.sub.2 or the like or SOG (spin on glass) is coated as an intermediate layer 52 and, as a top layer, an electron beam resist 53 is coated. Further thereon, an aluminum film 54 is formed by vapor deposition up to a thickness of about 100 angstroms in order to prevent charging-up (FIG. 6(a)). After exposure to light, the aluminum film 54 is removed with an alkaline solution, after which development is carried out (FIG. 6(b)). Then, using this resist pattern as a mask, dry etching of intermediate layer 52 is carried out (FIG. 6(c)). Next, bottom layer 51 is dry-etched, using the intermediate layer as a mask (FIG. 6(d)). By the above-mentioned multi-layer resist process, a fine pattern can be formed at a high aspect ratio. However, in a multi-layer resist prepared by vapor deposition of aluminum, the process is not practical because the process is more complicated and it involves the problem of contamination.